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I can't absorb everything right now, but I'd be happy to post little video of brazing when I do it next time.
It is quite an individual process tho. Ritchey does it with loads of heat in a sexy freestyle manner and Bilenky does it like he is drunk. Both end up with nice looking bikes. -
When I braze I only go off the condition of the flux, but I'm colour blind so colour of steel is not visible to me.
Silver would be my choice for capillary joints, as it flows so much better. Especially if you are new to it, pull the silver through in a way that it will be obvious that it has gone all the way through, so put silver in at the top and make sure it comes through at the bottom.
Fixturing is a personal process, but personally I don't like doing subassemblies on stuff like forks, wishbones etc as you have no idea whether you are in line for the plane you are not working on. Much better to tack everything in place then finish off all the joints in a logical fashion.
Bars, stems, seat mast toppers etc are all interference fit. The number of clamps you are suggesting should be sufficient. If you can try and get T45 tubing as you won't need to heat treat. Yes you can build a stem fixture free, but again that depends on how adept you are at Fixturing.
Racks should really be stainless, simply because if they aren't they would have to be painted, and the paint can wear off in use. I use 10mm tubing for racks, but make them rarely.
Stress testing is often a bit of a red herring, or at least it is in relation to how people on forums doing it. Hanging off a joint you have made and seeing where it fails doesn't really replicate how a bicycle frame would normally fail, it's to do with duty cycles. It will show you whether you have totally fucked said joint up, but beyond that you'll need a specific testing fixture.
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Hulsroy
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@FredyCro
Soaked up 18 pages of Q and A, so nice to see real frame builders sharing their knowledge :)
I am about to order some stuff for upcoming projects and would ask for your opinion beforehand, so here it goes.
First of is to get some practice lugs and tubing and do some lug and fillet brazing and stress test/cut/inspect everything, then I would like to build a fork, a stem and some racks. I will have access to an oxy-propane setup, TIG and a more experienced person as well as enough tooling to make it all possible.
Fork
It would be a basic 1" threadless fork with straight legs and a lugged crown (Max copy from ceeway and the hardware it goes with). Should we use silver or bronze filler since we are going to be using an O-P torch? How to recognize the point of no return (cooked joint), is charing the flux the only pointer besides steel changing the color to glowing orange (which seems to be the normal case in all the videos I watched)? Is it wrong to do it in 2 steps - braze in the legs, see if the filler flowed good and then do the steerer?
Brazed stem
I realize that this is a project for someone with an advanced experience, but I'd still like to try it, provided we manage to do some clean/strong fillets beforehand.
Tubing- I found some CrMo tubes for the steerer and the bar clamp part. Do I want the ID of the tubing to be exactly as big as the area that is going to be clamped to? What's the tolerance here? Do the tubes need to be machined internally? The tubing I found would be 1.5 mm thick and about the same diameter we are trying to achieve (1" fork, OS bars). What OD/wall thickness should we use for the main tube? I thought to use the practice CrMo that ceeway offers (either 28.6/0.8 or 31.8/1), any ideas here regarding stiffness? Also the clamp design, for simplicity sake I'd use the one bolt setup on the bar and double seat clamp on the steerer area. I guess the bar clamp needs to be filed with hand to make it fit nicely? Can it be done without a jig?
Rack
What tubing (8,10, 12?), mild steel or stainless? If stainless can we braze it with Sif1 or Sif2?
What size torch tips/filler for what? I actually thought to buy small quantities of different fillers (sif 1, sif 2, silver 39 or 43) in different sizes and try to figure out what works for what.
I'd also love a detailed video of fillet brazing. Most videos show only part of the process and don't really show what is going on. Maybe @Hulsroy could do a nice video next time he brazes with oxy-propane?
If anybody has useful links or PDF copies of frame building books, articles shoot me a PM. Thanks!